feat: uses new subsonic format as default

[jef]

Description

Also gets rid of warning that port must be int when it's default was a string.

Left over from #3449.

[sampsyo]

Awesome; thanks and good catch. 🚀

[jef]

Only took 6 months for me to go in and fix it 😆

[jef]

Welp, this is what i get for not having Python has my main language:

Traceback (most recent call last):
  File "/usr/bin/beet", line 11, in <module>
    load_entry_point('beets==1.5.0', 'console_scripts', 'beet')()
  File "/usr/lib/python3.8/site-packages/beets/ui/__init__.py", line 1267, in main
    _raw_main(args)
  File "/usr/lib/python3.8/site-packages/beets/ui/__init__.py", line 1254, in _raw_main
    subcommand.func(lib, suboptions, subargs)
  File "/usr/lib/python3.8/site-packages/beets/ui/commands.py", line 956, in import_func
    import_files(lib, paths, query)
  File "/usr/lib/python3.8/site-packages/beets/ui/commands.py", line 929, in import_files
    plugins.send('import', lib=lib, paths=paths)
  File "/usr/lib/python3.8/site-packages/beets/plugins.py", line 492, in send
    result = handler(**arguments)
  File "/usr/lib/python3.8/site-packages/beets/plugins.py", line 151, in wrapper
    return func(*args, **kwargs)
  File "/usr/lib/python3.8/site-packages/beetsplug/subsonicupdate.py", line 95, in start_scan
    url = format_url()
  File "/usr/lib/python3.8/site-packages/beetsplug/subsonicupdate.py", line 64, in format_url
    if url and url.endsWith('/'):
AttributeError: 'str' object has no attribute 'endsWith'

Making a PR to fix.